The goal of this research is to characterize, using an in vitro model and microanalytical techniques, the physicochemical processes that govern the caries process and to suggest what steps in this process may be most easily interrupted or reversed. The model consists of fluid filled isolated microwells (20 to 100 mu m in diameter) drilled into the tooth section just behind the natural surface. The microanalytical instruments used to study the fluid within the microwells consist of microelectrodes, micropipettes and a microspectrophotomer. This microwell model was used during the current grant period to study compositional changes within the fluid phase of a lesion during simulations of de- and remineralization. Conditions chosen for these simulations (performed both on enamel and teeth roots) were usually based on a study of the compostion of "plaque fluid" from single tooth sites. These simulations have provided valuable insight into the caries process, which to our knowledge, is not obtainable from other methodology. Specifically, these measurements have demonstrated that a model developed during the course of these studies can correlated nearly all the compositional changes occurring during the caries process. However, only a narrow range of conditions and tooth sites have been examined. In the proposed studies, these techniques will be used to perform a systematic analysis of the factors effecting de- and remineralization both in the lesion (smooth surface and fissure areas) and in the roots (cementum and dentin). In these studies the chemical compostion attained by the microwells during simulation will be correlated with the permselectivity, degree of demineralization, and physical location of experimental area. Additionally, the composition and thermodynamic solubility of the mineral removed from the microwell during sample preparation will be measured using techniques developed during the current grant period. In demineralization studies, conditions will be used in which different concentrations of ions (organic acids, fluoride, and "neural" salts [KCl]) in the "attacking" solution are employed. Hypotheses about lesion fluid conditions will be tested in simulations based on the in fluid will be employed to examine their remineralization efficacy. The further development of micro techniques, which allow rapid measurement of numerous ions in microscopic fluid volumes, will provide a valuable tool for dental research.